Metabolism and Growth of Bacteria-Felton Flashcards
Describe bacterial division.
oCells grow until they become “double-sized”. Then they undergo cell division, which yields two “single-sized” cells.
oAll the components of the cell must be duplicated before the cell can divide. This means that the cell must regulate and coordinate the biosynthesis of all its components. This includes the bacterial chromosome, which must be replicated.
What is a nucleoid?
The bacterial chromosome is a single large circular DNA molecule. It is supercoiled to form a compact structure called the nucleoid.
What is the origin of replication? What is the replication fork?
DNA replication starts at one fixed point on the bacterial chromosome, called the origin of replication. The moving site of replication is called a replication fork.
Describe bacterial DNA replication? Can more than one round of replication occur at one time?
o In most bacteria, DNA replication is bidirectional, with two replication forks diverging from the origin. They meet at the terminus to complete replication.
o In rapidly growing bacteria, a new round of replication may be initiated before the previous round is completed. Thus multiple replication forks may exist at one time.
How is DNA replication regulated? Describe the Replicon model.
o The frequency of initiation of DNA replication is regulated in response to increases in cell mass. Somehow the cell is able to “sense” its own mass and initiate replication when appropriate.
o Initiation of DNA replication is controlled by regulatory proteins which act at the origin of replication to prevent or allow formation of replication forks. This regulatory mechanism is called the replicon model.
What are the different planes of replication?
- When the planes are parallel = chains.
- When the planes are perpendicular = tetrads
- Another type results in an 8 cell cubiodal arrangement.
What nutrients can pass through the membrane?
o Hydrophobic molecules can pass directly through the cell membrane because they are lipid-soluble.
o Other very small molecules, such as water or ammonia, may pass directly through membranes by simple diffusion or osmosis. Most cells also possess aquaporins which allow more efficient passage of water molecules only.
How do larger molecules enter the cell?
Most other molecules, however, are blocked by the phospholipid bilayer and must use carrier proteins to cross the cytoplasmic membrane of both Gram positive and Gram-negative bacteria. Each molecule uses its own specific carrier. In general, these carriers transport their substrates by energy-dependent processes. But there are some examples in which a substrate is transported by its carrier in an energy-independent, passive process called facilitated diffusion.
What is active transport?
Active transport: energy obtained directly from the hydrolysis of ATP to drive the transport and accumulation of a substrate against its concentration gradient, and thus concentrate it inside the cell. The transported molecule is not chemically modified in the process.
What is group translocation?
Group translocation: energy-dependent process requiring specific carrier proteins. During group translocation, the nutrient molecule is modified (e.g. phosphorylated) during its transport into the cell. The modified molecule is unable to leave the cell. (ex. phosphotransforase system)
What is facilitated diffusion?
Facilitated diffusion: binding of the molecule to a specific protein carrier in the membrane and transport of the molecule across the membrane, but without expenditure of energy. In facilitated diffusion, the substrate moves down its concentration gradient (higher concentration outside, lower inside) as it is transported into the cell.
What are the energy sources for bacteria? Describe them.
o Most use organic molecules (reduced carbon) as sources of both carbon and energy.
oAutotrophic bacteria: use oxidized carbon (CO2) as main carbon source and photosynthesis or oxidation of reduced inorganic compounds as a source of energy and reducing power.
• Example: cyanobacteria.
o Heterotrophs: use organic molecules as both carbon and energy source.
• All pathogens are heterotrophs.
What are the reactions and products of respiration?
oGlycolysis: glucose → pyruvate + ATP + NADH
oTCA cycle: Pyruvate → CO2 + ATP + NADH
oETC → NADH → H2O + ATP
What is fermentation? What are the end products?
o Glucose and lactate are at the same redox level. However, lactate is at a lower energy level.
o This allows regeneration of NAD.
o End-products can be: lactate, acetate, ethanol and butyrate.
What are the methods of breaking down glucose?
o Glycolysis (Embden-Meyerhof) pathway
o Pentose phosphate pathway
o These 2 pathways differ in their other products and overall role.
o Entner-doudoroff pathway: less efficient than glycolysis. Yields 1 ATP/glucose.
